They have a very cushy welfare state for Saudi nationals and a vast underclass of impoverished and effectively enslaved workers who are from other countries and have no local resources. If their workers get uppity they can be shipped home, beaten in to compliance, or just starved. If the Saudi nationals get uppity the royals can cut them off from that sweet, sweet oil money. And if you're cut off you're fucked because there's nothing else to do in Saudi.

Think Immortan Joe in Mad Max - they control the water/oil/money